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Патент USA US2137010

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Nov., 15, 1938.
A. v. BEDFORD
2,137,010
TELEVISION SYSTEM
Filed June 9, 1954
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INVENTOR’
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NOV. 175, 1938.
A_ V, BEDFORD
'2,137,010
TELEVISION SYSTEM
Filed‘June 9, 1934
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INVENTOR
Alda VBedford
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`2,137,010
Patented Nov. 1_5, 1938
UNITED STATES PATENT OFFICE
TELEVISION SYSTEM
Alda v. Bodfora, Collingswood, N. J., assignor to
Radio Corporation of America, a corporation
of Delaware
Application June 9, 1934, Serial No. 729,730
3 Claims. (Cl. 178--7.2)
My invention relates to television systems and ture thereon to be transmtted is moved into posi
particularly to television systems which com
tion in a ñlm gate by means of a standard inter
mittent mechanism which is driven by a synchro
prise a cathode-ray transmitter tube and an elec
tric discharge tube generator of defiecting and nous motor connected to a 60 cycle power line.
Electrical impulses from the output of the im
3.1 synchronizing impulses.
pulse generator and electrical impulses derived
It has been found, in television systems utiliz
ing vacuum tube impulse generators, such as from the power line are fed into a common con
generators of the type disclosed in my copending trol circuit which changes the frequency of the
application, Serial No. 726,258, filed May 18, 1934, main oscillator of the impulse generator in re
where pictures are transmitted from a motion sponse to any phase shift of the impulses in said 10
picture film, that it is difficult to keep the pic» common circuit.
Other objects, features, and advantages of my
ture properly “framed”. 'I'his difficulty is caused
partly because of slight variations in the power invention will appear from the following descrip
line frequency, but mainly because of a tendency tion taken in connection with the accompanying
drawings, in which
of the impulse generator frequency to “drift”,
Figure 1 is a View of a television transmitter
I have discovered that the difiiculty in keeping
the picture framed may be overcome by operat
-embodying my invention,
ing the impulse generator in step or “locked in”
Fig. 2 is an end view of a shutter disc shown in
with the alternating current power source which
supplies power for the film drive.
Operating the impulse generator in step with
the power line has a further advantage in that
Fig. 1,
the frequency of the impulse generator output
ployed in the system shown in Fig. 1,
is maintained substantially constant, since the
5 frequency variations of the power line are so
slight that it is possible to use a television re
ceiver which does not require a “speed-control”
adjustment. In other Words, if all substantial
drift in the impulse frequency is prevented, there
is no need for an adjustment on the receiver for
changing the frequency of the vertical defiecting
oscillator to keep it under the control of the ver
tical synchronizing impulses.
An object of my invention is to provide an
improved television system in which pictures
transmitted from a ñlm are properly framed.
More specifically, an object of my invention is
to provide a. television system, utilizing an elec
tric discharge tube impulse generator, in which
40 pictures transmitted from a film are always prop
45
Fig. 3 is a group of curves which are referred 20
to in explaining my invention,
.
Fig. 4 is a circuit diagram of an amplifier em
Fig. 5 is a set of curves which are referred to in
explaining the operation of my control circuit, 25
and
Fig. 6 is a chart illustrating the operation of
the picture projector and scanner.
Referring to Fig. 1, a. television transmitter
system is illustrated which includes a cathode 30
ray transmitter tube I of the type described in
an article by Dr. V. K. Zworykin which appears
in the January, 1934, issue of The Journal of
The Franklin Institute. 'I‘his tube comprises an
evacuated envelope 3 having an electron gun 5,
a focusing and accelerating anode 1 and a mo
saic 9 of light sensitive elements thereon. De
fiecting means, such as defiecting coils II and I3,
are provided for defiecting the electron beam
horizontally and vertically, respectively, in order 40
erly framed.
to scan the mosaic 9 with the beam.
A further object of my invention is to provide
a television transmitter in which the frequency
of an electric discharge tube impulse generator
To produce the desired current flow through
the defiecting coils II and I3 for defiecting the
electron beam, an electric discharge tube impulse
generator is provided. This generator consists 45
is held substantially constant.
A further and more specific object of my inven
tion is to control the frequency of an electric
discharge tube impulse generator with respect
to the frequency of the current from a power line
50 or the like.
'
In one embodiment of my invention, a vacuum
tube impulse generator is utilized which has an
output suitable for interlaced scanning as de
scribed in my above-mentioned copending ap
55 plication.
A motion picture film having a pic
of a main oscillator I5 from which are derived
electrical impulses of the desired frequency for
horizontal deflection and also electrical impulses
of the desired frequency for vertical deflection.
The main oscillator I5 may be a blocking oscilla
50
tor consisting of an electrical discharge tube I1
having a cathode I9, a control grid 2l and an
anode 23. The control grid 2| is connected
through a variable grid leak resistor 25 and
through a resistor 21 in the control circuit (which 55
2
2,187,010
will be described hereinafter) to ground and
through ground to the cathode I9.`
The anode 23 is maintained at a positive po
My improved television system is especially de
signed, as will .be explained hereinafter, for the
transmission of pictures on a motion- picture film,
tential by means of a suitable voltage source such
as a battery 29 -which has its negative terminal
connected to the cathode l5 and its positive ter
minal connected through a resistor 3| and the
primary winding 33 of a transformer 35 to the
anode 23. A condenser 31 is connected in series
such a film being indicated generally at 55. The
with the secondary 33 of the transformer 35, the
condenser 31 and secondary 39 being connected
between the control grid 2l and the cathode I9.
The transformer windings 33 and 35 are so
phased that sfn increase in plate current in the
15. tube I1 causes the control grid 2l to become more
positive whereby grid current flows into the grid
condenser 31 to charge it in such a direction as
to apply a negative bias to the control grid 2l.
The plate current finally approaches its satura
20 tion value so that its rate of increase becomes
less, the voltage fed back to the grid decreases
whereby the plate current decreases, thus re
versing the phase of the voltage applied to the
control gri4 through the transformer 35 and
During the
time the grid has been positive, the condenser
has been charged sufficiently to hold the tube
25 biasing the tube I1 beyond cut-0H.
picture frames are moved intermittently into
position in a film gate 51 by means of a standard
intermittent 59. 'I'he intermittent 59 is driven
through a gear box 6I by a synchronous motor
53 at the standard speed whereby 24 pictures per
second are projected upon the mosaic_9. A shut 10
ter disc 55 is also driven by the synchronous
motor 53 through the gear box 5i, it being rotated
at 24 revolutions per second.
As shown in Fig. 2„the shutter disc 55 has two
openings 61 and 69 therein which are diametri
cally opposite each other for the purpose of cut
ting of! the light projected toward the mosaic
periodically, as will be more fully explained here
inafter.
For reasons previously mentioned, and particu-. 20
larly in order to keep the picture properly framed,
a control circuit 1i is provided for maintaining
the impulse generator locked in with the 60 cycle
power line 13 to which the motor 53 is connected.
The control circuit includes an electric discharge
tube 15 having a cathode 11, a control grid 19
and an anode 8l. The tube 15 is so adjusted that
it functions as a distorting amplifier or detector.
In one specific embodiment this is accomplished
by maintaining the control grid 19 at a high 30
biased beyond cut-off and no further oscillation
takes place until the charge has leaked off the
30 condenser 31 through the grid leak resistor 25
sumciently to lower the gridvoltage to a value - negative bias by> means of a biasing source, such
which again permits flow of plate current.
as a battery 83, the negative bias being high
’Ihe voltage impulses produced by the oscilla
enough to bias the tube beyond the cut-off poten
tor l5 are impressed upon a chain of frequency tial. 'I'he anode 8| is maintained at a positive
35 dividers Il, 43, 45, and 41, each of which may be a
potential by means of a source of potential, such 35
blocking oscillator operating the same as the as a battery 85, having its negative terminal con
main oscillator l5 but at a lower frequency. Each nected to the cathode 11 and its positive terminal
oscillator is locked in step with the oscillator of connected to the anode 8l through the resistor
next highest frequency. The circuit of the fre
21. The resistor 21 is shunted by a filter con
denser 81.
40 quency divider 4I is illustrated in order to illus
40
trate the invention more completely but a de
It will be noted that the resistor 21 is con
scription of the circuit is not believed to be neces~ nected in series with the grid leak resistor 25 of
sary in view of the description of the main oscil
the blocking oscillator l5 whereby any change in
lator circuit I5.
voltage drop across the resistor 21 causes a. change
The frequency of the main oscillator output is in the bias on the control grid 2l of the blocking
45
divided in two steps of three and two steps of oscillator. 'I'he filter condenser 81 has sufficient
five, as indicated on the drawings to produce capacity to integrate current impulses and cause
voltage impulses occurring at the rate of 48 per a substantially steady flow of current through the
second, this being the desired vertical deflecting resistor 21.
The current flow through the control circuit
50 or frame frequency. The 48 cycle impulses are
supplied to the input circuit of a saw-tooth Wave resistor 21 is caused to vary in response to a
generator 4I which converts them into voltage phase shift between frequency of the 60 cycle
impulses of the necessary shape for causing a current from the power line 13 and the frequency
flow of current, having a saw-tooth wave shape, of the impulse generator output by impressing
through the deflecting coils I3.
the impulses from both the power line and the
'I'he horizontal defiecting impulses are obtained impulse generator upon the input circuit of the
by impressing a portion of the output energy of control tube 15.
the main oscillator I5 upon the input circuit of
In order to effect the desired control, it is de
a frequency divider 5i which divides the fre
sired, in the specific embodiment illustrated, that
60 quency of the main oscillator output by two to
the two groups of control impulses occur at the
produce 5400 impulses per second. The output same frequency. Therefore, since current from
of the frequency divider 5| is impressed upon a the power line has a frequency of 60 cycles and
saw-tooth wave generator 53 which has its out
the impulses from the vertical deñecting circuit
put connected across the horizontal deñecting occur at the rate of 48 per second, the 48 cycle
65 coils Il for causing a iiow of saw-tooth wave impulses are impressed upon a frequency divider
current therethrough.
89 which lowers the frequency to 12 impulses per
It will be noted that the vertical deilecting and second. The output of the frequency divider 89
horizontal deflecting frequencies are such as to is impressed upon a wave shaping amplifier 9|
cause 1121/2 lines per picture frame, in order to and through a coupling condenser 93 upon the
70 provide interlaced scanning as described and control grid 19 of the tube 15.
claimed in my above identified copending appli
Current from the 60 cycle line 13 is impressed
cation. Although my invention is described in upon a frequency divider 95 which divides the
connection with an interlaced scanning system, frequency by five to produce impulses occurring
it should be understood that it is of general at the rate of 12 per second. Both the fre
76 application.
quency divider 95 and the frequency divider 89 75
3
2,137,010
may be blocking oscillators similar to the ones
described above. The impulses appearing in the
output circuit of the frequency divider 95 are
impressed upon a wave shaping amplifier 91
from lthe output of which they are fed into the
input 4circuit of the control tube 15 through a
transformer 99 in such phase that they add with
the 12 cycle »impulses from ampliñer 9|.
It should be understood that the wave shaping
10 amplifiers 9| and 91 may be omitted, if desired,
`particularly when the distorting or detector tube
15 is biased to cut-olf, as described. Also, if
- the power line or other control source provides
current at the proper frequency, the sine wave
current therefrom may be impressed directly
upon the control tube circuit 1| through the
transformer 99.
The operation of the control circuit 1| will be
better understood by referring to Fig. 3 which
shows the wave shape of the voltage impulses
appearing in the output circuit of a frequency
divider where it is a blocking oscillator. The
voltage waves indicated at |0| and |03 are typi
cal of the voltage impulses generated by a block
ing oscillator. It will be noted that each wave
includes a sharp positive impulse, this impulse
being the one which is used for control purposes.
, The wave shaping amplifiers 9| and 91 cut od
the portion of the voltage wave which appears
30 below the dotted line |05. A preferred circuit
for these wave shaping amplifiers is shown in
Fig. 4.
Referring to Fig. 4, the amplifier consists of
two resistance coupled amplifier stages, the first
stage comprising an electric discharge tube |01
which is biased beyond the cut-off potential by
means of a biasing battery |09. In the par
ticular embodiment illustrated, the second am
pliñer stage includes an electric discharge tube
40 ||| which is biased to function as a non-distort
ing amplifier. 'I‘he first amplifier stage |01 per
mits the passage of only the positive peak of the
blocking oscillator voltage wave, that is, the
portion of the wave above the dotted line |05,
while the second stage simply amplifies this im
pulse and reverses its phase so that it appears in
the output of the amplifier ||| as a positive
voltage impulse.
The two voltage impulses which are supplied
from the wave shaping amplifiers 9| and 91 ap
pear in the input circuit of the control tube 15
as shown at ||3 and ||5 in view a of Fig. 5.
These voltage waves add to give a resultant
wave ||1 which is shown in view b of Fig. 5.
The grid lvoltage-plate current characteristic
of the tube 15 is shown at ||9 in view c of Fig. 5.
Following conventional graphical construction,
it is seen that the voltage wave ||1 impressed
upon the input circuit of the tube 15 causes a
flow of plate current in the output circuit of
the tube which has the wave shape indicated at
|2|. These impulses |2|, which occur in the
which is represented by the dotted line curve |21
in view d of Fig. 5. It is evident that, as a re
sult of the frequency shift, less energy is sup
plied to the filter condenser 91 and there will be
a corresponding reduction in current flow I
through the resistor 21 whereby the bias voltage
on the control grid 2| of the blocking oœillator
tube |1 will be changed and the frequency of the
blocking oscillator l5 will be corrected.
In order to explain more in detail how the 10
frequency of the blocking oscillator I5 is cor
rected, it will be assumed that the voltage or'
control impulses ||3 and H5, shown in Fig. 5,
are the impulses derived from the power line and
from the oscillator, respectively. Also, assume
that the oscillator frequency decreases to shift
the oscillator control impulse to the position
shown by the dotted curve |29.
As previously ex
plained, this causes less current to flow through ‘
the resistor 21 whereby the negative potential 20
applied to the control grid 2| of the oscillator I5
is decreased to increase the oscillator frequency
to its original value. Attention is called to the
fact that the oscillator control impulse is not
brought back to its original phase relation with 25
the power line control impulse H3; instead, an
equilibrium point is reached where a new phase
relation between the control impulses causes the
proper bias to be applied to the oscillator.
It will be understood that the frequency of 30
the main oscillator I5 may be controlled by
the control circuit 1| in various other ways than
the particular one illustrated. For example, the
voltage drop across the resistor 21 may be uti
lized to change the potential on the anode 23 of
the blocking oscillator tube |1 or it may be uti--v
lized to control the voltage on a second grid elec
trode, not shown. Also, the control impulses
applied to the control circuit need not have the
same frequency so long as they bear a. whole
number multiple frequency relation to each other,
as in the case of one group of impulses occurring
at twice the frequency- of the other group.
It will be apparent from the foregoing descrip
tion that the control circuit` 1| and its asso 45
ciated circuits causes the mosaic 9 to be scanned
synchronously with the projection of the picture
frames thereon. The picture projection! and
scanning operation is illustrated on the chart in
Fig. 6. Starting with the condition just as the
shutter opening 51 rotates opposite the picture
projector, the picture is projected upon the
mosaic 9 at the time A and remains thereon
until the time B, at which time the shutter 55 in«~
tercepts the beam of light from the projector. 55
During this time, the cathode ray has been
brought to its starting position for scanning and
the film has been stationary. At the time B, the
cathode ray starts scanning the mosaic and com
pletes the scanning at the time C, the film being 60
stationary during this scanning period and there
being no light upon the mosaic.
At the time C, the second shutter opening 99
rotates into position opposite the projector to
permit the picture to be again ’projected upon 65
the mosaic until the time D. at which time the
light is again intercepted by the shutter 55. At
this time, the cathode ray again begins to scan
output circuit of the tube 15 at the rate of 12
per second, charge the filter condenser 81 to
produce the substantially steady flow of current
through the resistor 21 previously referred to.
Assume that either the frequency of the main
blocking oscillator i5 or the frequency of the
power line 13 changes to cause the voltage im . the mosaic 9, the mosaic again being dark. Up
70
pulses to move farther apart as indicated by the to this time, the iìlm has remained stationary.
Beginning at the time D, the intermittent 59
dotted line curve |23 in Fig. 5. The two control
impulses now add to give the resultant voltage starts to move the next picture frame into posi
shown by the dotted line curve |25 in view b of tion, At the time E, the next picture frame has
Fig. 5, and this voltage produces a current flow been moved into position and the intermittent
stops. ‘I'he scanning of the dark mosaic con- 75
75 in the output circuit of the control tube 15
4
2,137,010
tinues until the time A. ai' which time the first
shutter opening 51 again moves into position op
poslte the projector and the second picture frame
is projected upon the mosaic.
'I'he picture signals appear across a resistor |29
connected between >the mosaic 9 and the second
anode 1 and are impressedv upon the picture
signal amplifier III which amplifies them and
impresses them upon a radio transmitter |33 or
upon a transmission line (not shown).
In order to maintain the scanning at the re
ceiver synchronized with the scanning at the
transmitter, the horizontal synchronizing im
pulses are impressed through a wave shaping
15 amplifier |35 upon a suitable point in the picture
signal amplifier |3I.
Likewise the vertical de
fìecting impulses are impressed through a wave
shaping »amplifier |31 upon a suitable point in
oscillator, means for obtaining a voltage wave
from an alternating current source, means for
moving a film having a picture thereon to be
transmitted, said means including a synchronous
motor connected to said source, means for pro
jecting the pictures of said film upon said mosaic,
means for obtaining control impulses having a
fixed frequency relation to said vertical deflect
ing impulses, means for impressing said control
impulses and said voltage wave upon a common 10
circuit, means for producing a substantially
steady current having a value depending upon
the phase relation of said control impulses and
said wave in said common circuit, and means for
controlling the frequency of said oscillator in ac
cordance with the value of said substantially
steady current.
-
the picture signal amplifier |3I. Preferably,
20 the horizontal and vertical synchrozing impulses
2. In a television system including a cathode
ray transmitter tube having a mosaic of elec
are impressed upon such a stage in the ampli
fier |3| that they appear at the receiver with a
including an oscillator for generating compara
polarity opposite to the polarity of the picture
signals in the white direction whereby the syn
25 chronizing signals and picture signals may be
more easily separated.
The wave shaping amplifiers |35 and |31 may
be the same as the amplifier shown in Fig. 4 ex
cept that it is preferred to adjust the plate re
30 sistor of the first tube such that. the signal
strength on the grid of the second tube I I I causes
the grid to cut off the plate current of the second
tube near the peaks of the negative swing. With
the Wave shaping amplifiers so adjusted, the
lower portion of each blocking oscillator impulse
is cut off as indicated by the dotted line |05 in
Fig. 3 and the peak of the impulses is also cut
off by the second ampliiier stage || as indicated
by the dotted line |39. By so shaping the syn
40 chronizing impulses before they are impressed
upon the picture signal amplifier |3|, interfer
ence with the picture signals is avoided. It will
be understood that in accordance with usual
practice, the horizontal synchronizing impulses
45 are transmitted at the end of each scanning line
while the vertical synchronizing impulses are
transmitted at the end of each picture frame
whereby the picture signals and the synchroniz
ing signals are not transmitted simultaneously.
50
From the foregoing description it will be un
derstood that various modifications may be made
in my invention without departing from the
spirit and scope thereof and I desire, therefore,
that only such limitations shall be imposed there
55 on as are necessitated by the prior art and set
forth in the appended claims.
I claim as my invention:
1. In a television system including a cathode
ray transmitter tube having a mosaic of elec
60 tron emissive capacity elements therein, means
for generating horizontal and vertical deiiecting
impulses for said tube, said means including an
tron emissive capacity elements therein, means
tively high frequency horizontal defiecting im
pulses and comparatively low frequency vertical
defiecting impulses for defiecting the cathode
ray in said tube, means for obtaining compara
tively low frequency control impulses from said
oscillator, means for obtaining periodic voltage
25
pulses from an alternating current power source,
means for intermittently moving a film having
a picture thereon to be transmitted, said means 30
including a synchronous motor connected to said
power source, means for projecting a frame of
said `film upon said mosaic when said film is sta
tionary, and means for controlling the frequency
of said oscillator in accordance with the phase
difference of said control impulses and said volt
age impulses.
3. In a television system in which a picture is
to be projected upon an electron emissive screen
surface and in which an electron stream is to be
deflected both vertically and horizontally, means
for generating horizontal and vertical defiecting
impulses for producing said deflection, said
means including an oscillator, means for ob
taining a voltage wave from an alternating cur
rent source, means connected to the power sup
ply for moving a film having pictures thereon
with a motion having a predetermined relation
to the frequency of said alternating current,
means for projecting the pictures of said film
upon said screen surface, means for obtaining
control impulses having a fixed frequency rela
tion to said vertical deñecting impulses, means
for impressing said control impulses and said
voltage wave upon a common circuit, means for
producing a substantially steady current having
a value depending upon the phase relation of
said control impulses and said wave in said com~
mon circuit, and means for controlling the fre
quency of said oscillator in accordance with the
value of said substantially steady current.
ALDA V. BEDFORD.
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